fix broken callbacks - deal with Julia pickiness in assigning C_NULL to PyPtr

Author: stevengj

src/PyCall.jl

@@ -86,7 +86,7 @@ function pydecref(o::PyObject)
     if initialized::Bool # don't decref after pyfinalize!
         ccall((@pysym :Py_DecRef), Void, (PyPtr,), o.o)
     end
-    o.o = C_NULL
+    o.o = convert(PyPtr, C_NULL)
     o
 end
 

src/callback.jl

@@ -43,13 +43,13 @@ function jl_Function_call(self_::PyPtr, args_::PyPtr, kw_::PyPtr)
         f = unsafe_pyjlwrap_to_objref(self_)::Function
         ret = PyObject(f(convert(PyAny, args)...))
         ret_ = ret.o
-        ret.o = C_NULL # don't decref
+        ret.o = convert(PyPtr, C_NULL) # don't decref
     catch e
         ccall((@pysym :PyErr_SetString), Void, (PyPtr, Ptr{Uint8}),
               (@pysym :PyExc_RuntimeError),
               bytestring(string("Julia exception: ", e)))
     finally
-        args.o = C_NULL # don't decref
+        args.o = convert(PyPtr, C_NULL) # don't decref
     end
     return ret_::PyPtr
 end

src/pytype.jl

@@ -332,7 +332,7 @@ function pyjlwrap_repr(o::PyPtr)
     o = PyObject(try string("<PyCall.jlwrap ",unsafe_pyjlwrap_to_objref(o),">")
                  catch "<PyCall.jlwrap NULL>"; end)
     oret = o.o
-    o.o = C_NULL # don't decref
+    o.o = convert(PyPtr, C_NULL) # don't decref
     return oret
 end